When communication between a base station and, for example, a communication apparatus functioning as a mobile-station is performed by, for example, WiMAX (Worldwide Interoperability for Microwave Access), ranging (Ranging) is performed. The ranging between the base station and the communication apparatus is performed by, for example, synchronizing communication between the base station and the communication apparatus, adjusting a transmission power level of the communication apparatus, and maintaining a quality of a communication link.
The communication apparatus transmits, prior to ranging, a ranging code, which is a code for transmission control, to the base station. The base station identifies the communication apparatus on the basis of received ranging code, and transmits a ranging response message to the identified communication apparatus. This ranging response message includes the ranging code which the base station received, an adjustment parameter such as a transmission power level, and information (status information) indicating whether or not the ranging is finished.
The communication apparatus adjust the transmission power level or the like on the basis of the adjustment parameter of the received ranging response message. After this adjustment, the communication apparatus again transmits the ranging code to the base station to confirm whether the adjusted transmission power level is appropriate.
A series of the above processes are repeatedly performed between the base station and the communication apparatus, and the communication apparatus, when receiving ranging termination information (success information) from the base station, aborts transmission of the ranging code and terminates the ranging. Thereafter, the base station performs processes such as an assignment of CID (Connection Identifier) to the communication apparatus which has terminated the ranging, and keeps the communication apparatus under control, thus a communication link being established.
Here, this ranging code is generated by the communication apparatus on the basis of a ranging code generating parameter transmitted by broadcasting from the base station. The ranging code has 256 patterns as usable code patterns, wherein each ranging code consists of 144 bits and is generated by a pseudo random binary sequence (PRBS) generator.
FIG. 1 is a transmission and reception timing diagram of radio frames transmitted or received when communication is performed between the base station and the communication apparatus (the mobile-station).
FIG. 2 is a timing diagram illustrating generation and transmission processes of the ranging code performed by the communication apparatus. Timings T1 through T4 of FIG. 2 respectively correspond to the timings T1 through T4 of FIG. 1.
The communication apparatus, when starting communication with the base station, receives, at the timing T1 of FIG. 1, a down-link sub-frame (abbreviated as “DL sub-frame” hereinafter) transmitted from the base station. Then, as illustrated in FIG. 2, a MAC (Medium Access Control) unit of the communication apparatus parses an UCD (Uplink Channel Descriptor) of the DL sub-frame (process S1), obtains an UL_Permbase (Uplink_Permutationbase) information specified by the UL-MAP which already has been received, and obtains a ranging code generating parameter GP. Further, the MAC unit continues this parsing until obtaining the specification data D of the ranging code from the DL sub-frame.
An UL_PHY (Uplink Physical Layer) unit generates from this generating parameter, by using, for example, the PRBS generator, 256 pieces of ranging codes each consisting of 144 bits one after another, and stores these in a memory (process S2 of FIG. 2).
Further, at the timing T2, the communication apparatus does not perform a transmission process of data related to the ranging by using up link sub-frame (abbreviated as “UL sub-frame” hereinafter). Similarly, at the timing T3, data process related to the ranging with regard to the received DL sub-frame.
The MAC unit of the communication apparatus consecutively performs parsing the UCD (process S3 of FIG. 2), and receives (obtains) specification data D of the ranging code. The specification data D is data for the base station to specify any one of the 256 pieces (patterns) of the ranging codes and to command the communication apparatus to transmit the specified ranging code to the base station.
The UL_PHY unit of the communication apparatus reads out a ranging code for transmission corresponding to the specification data D from among the 256 pieces of ranging codes stored in the memory, and transmits the read out ranging code to the base station. Hereafter, on the basis of this ranging code, a ranging is performed between the base station and the communication apparatus. Here, the number of bits of the ranging code, and the number of pieces to be generated are illustrative examples.
As above, the UL_PHY unit of the communication apparatus previously generates 256 pieces of the ranging codes possibly specified by the specification data before receiving the specification data, and stores the ranging codes into the memory. The reason for that is that, within a certain period of time after the reception of the specification data, it is required to transmit the ranging code corresponding to the specification data to the base station.
For example, assumption is made such that, in response to the specification data D received (obtained) at the timing T3, the communication apparatus transmits the 250th ranging code specified by the specification data D at the timing T4. In this case, if the communication apparatus starts generating the ranging code corresponding to the specification data D at the timing T3 at which the specification data is received (process S5 of FIG. 2), the communication apparatus takes long time before generating the 250th ranging code and is not able to transmit the ranging code to the base station by the timing T4 for transmission.
Here, the previously described memory needs a capacity for storing 256 pieces of 144 bit ranging codes, which is at least about 4.6 K Byte (144 bit*256/8). Also, since the communication apparatus is capable of transmitting at most three types of the ranging codes, the memory capacity as much as three times of the above, which is at most about 13.8 K Byte (4.6 K Byte*3), is required. As such, using the memory capacity as much as about 13.8 K Byte solely for transmitting the ranging code is unproductive.